Multec 3.5 Fuel Injector Application Manual Product Description
Delphi Energy and Chassis Systems
Revision: 11/05-1 3-13
circuit switches the ground side of the driver circuit to control the injector
operation.)
3.6.3 Driver Circuit Clamping Voltage
When the injector driver circuit switches off the injector, the collapse of
the magnetic field in the solenoid coil generates a return voltage spike in
the circuit that must be dissipated. A Zener diode is used to limit EMI
radiation. Zener diodes with a breakdown voltages ranging from 56V to
100V can be used for injector performance characterization at Delphi.
Injector dynamic flow rate will vary with driver circuits set at different
clamping voltages. The Zener diode breakdown voltage used by the
vehicle controller should be employed for injector flow testing used to
generate vehicle calibration tables
3.6.4 Injector Polarity
See section 4.4.3.
3.7 Injector Flow Rate Sizing
The injector flow rate must be sized to provide adequate fuel flow for all
anticipated vehicle operating conditions. This will require knowledge of
the engine and platform performance requirements. In selecting the
proper injector flow rate, a balance must be maintained between the
maximum and minimum fuel rate requirements for the engine. To size the
injector, the following performance specifications must be determined:
1. Fuel system pressure
• Fuel system pressure information will be used to determine
director hole size.
• The Multec 3.5 injector magnetic circuit is designed for system
operating pressures of 300 kPa to 500 kPa (43.5 psi to 72.5 psi.)
• The fuel supply system should be designed to include pressure
relief to prevent the injector from being exposed to pressures
greater than 1000 kPa (145 psi.) Pressure in excess of 1000 kPa
may cause temporary loss of function, and possible permanent
damage.
Often it is desirable to determine the impact of a change in fuel system
pressure on flow. The following equation is given as an approximation for
estimating static flow at a given pressure drop when the static flow at a
different pressure drop is already known:
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